Building deb packages. Having a lintian issue.

Hi,
I have an OMV 4 machine that does double duty as a Debian package builder (nothing to do with OMV).
After a build I run lintian against the new pkg. When running a build on my OMV 4 machine I consistently get this in my lintian output:
'Opening configuration file /etc/apt/apt.conf.d/99openmediavault-proxy - ifstream::ifstream (13: Permission denied)'

As I say, the packages have nothing to do with OMV, and that file is completely empty.
Can anyone point me in the direction of a resolution? I don't know OMV very well (and I come from Ubuntu) so I'm not really sure where to start.
Thanks very much

Thanks for the quick reply.
Perms are indeed 640.

I have just noticed that I get the same response when I do something like 'apt search unzip' (note that I ran this as a regular user).
I suspect that the problem revolves around the fact that I use fakeroot to run lintian. My preference is to keep it that way.

What I don't understand (and you'd be the person most likely to know I suppose) is why that file? There are 5 other '99' prefixed files in that directory? And, is there a straightforward way around it?

Cheers!

Thanks so much! That seems to have sorted it out.
Cheers!